The discovery of new materials with novel chemical and physical properties often leads to the development of new and useful technologies. Over forty years ago, for example, the preparation of single crystal semiconductors transformed the electronics industry. Currently, there is a tremendous amount of activity being carried out in the areas of catalysis, superconductivity, magnetic materials, phosphors, nonlinear optics and high strength materials. Unfortunately, even though the chemistry of extended solids has been extensively explored, few general principles have emerged that allow one to predict with certainty composition, structure and reaction pathways for the synthesis of such solid state compounds, compositions or structures. Moreover, it is difficult to predict a priori the physical properties a particular three-dimensional structure will possess.
Clearly, the preparation of new materials with novel chemical and physical properties is at best happenstance with our current level of understanding. Consequently, the discovery of new materials depends largely on the ability to synthesize and analyze new materials, compounds, compositions or structures. Given approximately 100 elements in the periodic table that can be used to make such compositions consisting of three, four, five, six or more elements, the universe of possible new compounds remains largely unexplored. As such, there exists a need in the art for a more efficient, economical and systematic approach for the synthesis of possibly new compounds, compositions or structures (e.g., materials) and for the screening of such materials for useful properties.
One of the processes whereby nature produces molecules having novel functions involves the generation of large collections (libraries) of molecules and the systematic screening of those libraries for molecules having a desired property. An example of such a process is the humoral immune system which in a matter of weeks sorts through some 1012 antibody molecules to find one which specifically binds a foreign pathogen (Nisonoff, et al., The Antibody Molecule (Academic Press, New York, 1975)). This notion of generating and screening large libraries of molecules has been applied to the drug discovery process. The discovery of new drugs can be likened to the process of finding a key that fits a lock of unknown structure. One solution to the problem is to simply produce and test a large number of different keys in the hope that one will fit the lock.
Using this logic, methods have been developed for the synthesis and screening of large libraries (up to 1014 molecules) of peptides, oligonucleotides and other small molecules. Geysen, et al., for example, have developed a method wherein peptide syntheses are carried out in parallel on several rods or pins (see, J. Immun. Meth. 102:259–274 (1987), incorporated herein by reference for all purposes). Generally, the Geysen, et al. method involves functionalizing the termini of polymeric rods and sequentially immersing the termini in solutions of individual amino acids. In addition to the Geysen, et al. method, techniques have recently been introduced for synthesizing large arrays of different peptides and other polymers on solid surfaces. Pirrung, et al., have developed a technique for generating arrays of peptides and other molecules using, for example, light-directed, spatially-addressable synthesis techniques (see, U.S. Pat. No. 5,143,854 and PCT Publication No. WO 90/15070, incorporated herein by reference for all purposes). In addition, Fodor, et al. have developed, among other things, a method of gathering fluorescence intensity data, various photosensitive protecting groups, masking techniques, and automated techniques for performing light-directed, spatially-addressable synthesis techniques (see, Fodor, et al., PCT Publication No. WO 92/10092, 15 the teachings of which are incorporated herein by reference for all purposes). Despite these advances, most of the combinatorial work heretofore has focused on solid state-synthesis of materials. See also, e.g., U.S. Pat. Nos. 5,288,514 and 5,424,186.
Solution-based methods, such as the sol-gel process, are widely used for the synthesis of inorganic materials. One of the inherent advantages of the solution process for inorganic materials, as opposed to solid-state synthesis methodologies, is that diffusion distances are shortened due to the more intimate mixing that the solution offers. The solution-based methodologies usually result in a reduction in processing temperatures. Possibly, solution-based methodologies provide access to kinetically stable phases that might not otherwise be prepared through solid-state synthesis methodologies. Thus, a need exists for using a solution-based method for the synthesis of inorganic and other solid state materials.
This invention provides methods for the synthesis of combinatorial libraries or arrays on or in suitable substrates by effectively utilizing solution-based techniques. The invention can be used to make known materials or new materials. In addition, this invention provides a general route for the synthesis of transition metal and other oxides.